In recent years, in a cellular mobile communication system, it has been becoming a common practice to transmit not only sound data but also large-volume data such as static image data and moving image data along with implementation of multimedia information service. In order to realize large-volume data transmission, studies have been actively conducted on a technique for realizing a high transmission rate by utilizing a high frequency wireless bandwidth.
However, when a high frequency wireless bandwidth is utilized, a high transmission rate can be expected at a short distance but attenuation is increased in accordance with a transmission distance as the distance is long. Hence, when a mobile communication system in which a high frequency wireless bandwidth is utilized is actually placed in operation, a coverage area of a wireless communication base station apparatus (hereinafter abbreviated as a “base station”) is reduced, and therefore, there arises the necessity for installation of a larger number of base stations. Since the cost of installation of base stations is considerably high, there is a strong demand for a technique for realizing communication service that utilizes a high frequency wireless bandwidth while suppressing an increase in the number of base stations.
To satisfy such a demand, studies have been conducted on a relay transmission technique in which a wireless communication relay station apparatus (hereinafter abbreviated as a “relay station”) is installed between a base station and a wireless communication mobile station apparatus (hereinafter abbreviated as a “mobile station”) so as to increase a coverage area of each base station, and communication between the base station and the mobile station is performed via the relay station. FIG. 17 is a schematic diagram illustrating an overall configuration of a relay system in a related art. With the use of the relay technique illustrated in FIG. 17, a terminal (mobile station 20), which is unable to directly communicate with a base station 10, is also allowed to communicate with the base station 10 via a relay station 30. Note that a mobile station 21 is a terminal subordinate to the base station 10.
[Description of TD Relay in TDD]
Further, as a method for dividing links into an uplink (UL) and a downlink (DL), a TDD system is known. In the TDD system, links are divided into an uplink (UL) and a downlink (DL) in a time-division manner. Referring to FIG. 18, general outlines of a relay system in which a relay station is applied in the TDD system will be described below. FIG. 18 is a conceptual diagram of the relay system in which a relay station 30 is applied in the TDD system.
As illustrated in FIG. 18, the relay station 30 (RN) uses part of resources, allocated to an uplink (UL), and part of resources, allocated to a downlink (DL), to transmit/receive data to/from a base station 10 (eNB), and during this period, the relay station 30 (RN) suspends service provided to a mobile station 20 (UE2) connected to the relay station 30 (RN). FIG. 18 illustrates an example in which subframes #2 and #3 are uplink (UL) subframes serving as subframes for the uplink, and subframes #4 and #5 are downlink (UL) subframes serving as subframes for the downlink. In this example, the subframes #3 and #4 are used to perform communication between the relay station 30 (RN) and the base station 10 (eNB) through the uplink (UL) and the downlink (DL), respectively.